This invention relates in general to torque transmitting couplings. In particular, this invention relates to an articulating torsional coupling having a constant velocity output characteristic and an axial plunge capability.
Torque transmitting couplings are typically provided to accommodate power transmission and angular misalignment between two rotating shafts. These couplings often use bearing or bushing elements to permit articulation of input and output components as the shafts rotate. Different coupling designs exhibit particular operating and performance characteristics that limit their application to certain environments. The universal joint, also known as a Cardan or Hooke's Joint, is a two-plane hinge joint having a first plane connected to an output shaft and a second plane connected to an input shaft. A journal cross defines these planes, which are usually oriented at right angles. The journal cross typically terminates in four bearing elements that are mounted to yokes, each yoke lying in one of the first and second planes. A Cardan joint is capable of providing a substantially high power density within a compact rotational envelope, referred to as the “swing diameter.” These joints are also durable and, because of the orientation of the bearings and sealing elements, are very damage tolerant, particularly when impinged upon by debris. However when operating at an angle, the Cardan joint produces a non-uniform rotational output characteristic when provided with a uniform input characteristic. This non-uniform rotational characteristic results in the output shaft speeding up and slowing down twice every revolution, resulting in creation of vibration disturbances. The magnitude of this torsional disturbance increases with angle and rotational speed. Because of this condition, operating angles of Cardan joints are often limited to keep torsional disturbances within acceptable limits for a given application.
Other coupling designs are known that address the vibration disturbance issue of a Cardan joint. These couplings utilize various designs to produce a constant or near constant velocity ratio between the input and output shaft speeds relative to the misalignment angle. One broad category of constant velocity joints (CVJs) are the “ball-type” CVJs. These CVJs are the most common variety and rely on concentric input and output bearing races that transmit torque and accommodate angular movement through ball bearing elements. By orienting the ball bearing elements within the homokinetic plane, these joints provide constant velocity motion throughout their articulation range, which may be as high as 45 degrees, or greater. Some of these CVJs have a fixed center while other designs are capable of accommodating axial movement. The most common examples of these ball-type CVJs are the Rzeppa joint, cross-groove joint, and double offset joint. While these joints reduce or eliminate torsional disturbances, they can generate a higher amount of heat due to the ball bearing elements exhibiting both rolling and sliding motion as the joint rotates at an angle. This condition worsens as the torque, speed and angle operating parameters increase. In addition, the most common sealing element for these joints is an elastomeric boot that is often exposed to road debris. Once the boot is torn, these CVJs become quickly contaminated and exhibit a significantly reduced operating life.
Both Cardan joints and ball-type CVJs have limited articulation angles which can restrict the design of the systems to which they are applied. For example, the range of suspension movement in a vehicle, particularly an off-road vehicle, is limited to prevent over-angulation of the halfshafts that connect the axle differential to the wheel ends. Other types of joints that exhibit constant velocity characteristics, such as link-type couplings, have been known for some time. While these joints can be made to articulate at relatively high angles, they suffer from durability issues. These issues are due to the component designs deemed necessary to permit high operating angles without articulated component interference. Thus, prior link-type CVJs have not provided the power density necessary to permit their use in high load and space restricted applications, such as automotive powertrains. Thus, it would be desirable to provide a torque transmitting coupling that provides a constant velocity input to output ratio, accommodates a large articulation angle, and exhibits increased durability with reduced damage exposure.